1. Field of the Invention
The present invention relates to injectors and nozzles, and more particularly to injectors and nozzles for atomizing liquids.
2. Description of Related Art
Enabling the breakup of large liquid bulk flow into finely atomized droplets has always been a challenge, particularly in fuel injection applications. For simplex pressure atomizers, in order to obtain high flow rates, the liquid supply pressure must increase dramatically, or the orifice must be enlarged. Often high pressure is not feasible, and droplets get larger as the orifice diameter increases. Air assist or prefilming air-blast nozzles are commonly used to atomize sprays when pressurized air is available. The air-blast method relies on the shearing effect of high velocity air to provide atomization. Often, an upstream trim orifice is incorporated which aids in flow calibration. The pressure drop taken across the trim orifice wastes energy which could potentially be used for atomization.
In some cases, multiple injection points have been employed to disperse a flow, reducing each stream to a more manageable volume. However, there tend to be downsides to conventional multiple injection techniques, such as complex geometry, large part count, limited physical space, maintaining balanced flow rate at all injection points, poor downstream patternation, small passage sizes prone to plugging, external carbon build up due to wetted surfaces, and difficult heat shielding configurations.
In some known applications of multiple injection point injectors, jets of fuel are injected radially into a flowing air stream, relying on the air flow to break up the fuel stream. An example of this configuration is shown and described in European Patent Application No. EP 1 193 450. In this example, no swirl is imparted to the spray, which reduces design complexity, but causes fuel to emerge from the spray orifices as a straight jet, limiting atomization.
Another conventional type of injector with multiple injection points is fabricated by etching passageways into metal sheets and then bonding the sheets together, forming a laminated assembly. An example of this configuration is shown and described in U.S. Pat. No. 6,533,954. In this example, swirling air is introduced radially around each injection point, through slots in the laminated sheets. An inherent problem with this type of construction is the difficulty in heat shielding the fuel when the air is hot, as it is in most combustion and fuel processing applications, since the passageways for both air and fuel are formed from common sheets of metal creating high heat transfer rates between the hot air and colder fuel.
Another method of multiple point injection is to mount individual spray tips on stems attached to a manifold. An example of this type of configuration is shown in U.S. Pat. No. 6,755,024. In this example, each spray tip includes an air swirler to aid in atomizing fuel exiting the discharge orifice thereof.
Such conventional methods and systems generally have been considered satisfactory for their intended purpose. However, there still remains a continued need in the art for multi-point injectors that allow for effective atomization with simplified geometry, improved piece count and physical space requirements. There also remains a need for multi-point injectors that provide improved balance of flow rate, improved downstream patternation, simplified heat shielding capabilities, reduced plugging and reduced external carbon build up. The present invention provides a solution to these problems.